Gun barrels are traditionally manufactured from various steel alloys. Lining the gun barrels with various other materials to provide enhanced corrosion resistance, increased projectile velocity, and lengthened service life has been a routine practice for small arms for over 100 years.
Increased use of hotter burning gunpowder to increase projectile performance and fully automatic firing to increase rounds per minute cause gun barrels to reach temperatures exceeding 800° F. Maintaining gun barrel integrity and minimizing erosion to prolong gun barrel life has become very challenging under these conditions.
416 Society of Automotive Engineers (SAE) grade stainless steel has been used for gun barrels to prevent corrosion, but is generally not as well suited for use as a gun barrel compared to 4140 SAE grade and 4150 SAE grade chromoly steels. Chromoly steels provide better strength at the high temperatures reached during extended periods of fully automatic firing, which makes them very popular for use in military small arms such as the M-16 rifle.
Unfortunately, chromoly steels are vulnerable to corrosion and rapid erosion. Barrel bore rusting caused weapon malfunctions during the Vietnam War because the 4150 SAE grade chromoly steel barrels rusted in the humid environment. It was also learned that the high-pressure projectile fired by the M-16 rapidly eroded the chamber of the barrel. A chrome lining was applied to the barrel in order to extend the weapon's surface life.
Chrome-lined barrels present several of their own problems, though. First, it is very difficult to apply the chrome evenly in large production runs. Inconsistent application adversely affects the rifle's accuracy. Chrome lining also prevents the barrel from operating at temperatures exceeding 800° F. for any prolonged period of time, which limits the number of rounds that can be fired before the gun barrel must be permitted to cool. Otherwise, the barrel will lose its temper quickly, resulting in erosion of the barrel chamber and firearm malfunctions.
Other linings, such as the one described in U.S. Pat. No. 7,197,986, have been proposed, but they do nothing to increase the strength of the barrel at higher temperatures. The coating described is limited to protecting the chamber and rifling of the barrel. However, when a firearm is operated for long periods of time at high temperatures, preserving the temper of the barrel itself is the primary problem that must be overcome.
Alternative barrel materials, such as the composite gun barrel described in U.S. Pat. No. 6,889,464, provide a lightweight alternative to steel that cools faster than a standard gun barrel. Unfortunately, the resins used in the gun barrel's construction are not suitable for sustained high rates of fire. Eventually, the high heat generated causes the resin to break down, rendering the gun barrel unusable.
It is therefore an object of this invention to provide a gun barrel that maintains its temper and has increased corrosion resistance for extended operation of fully automatic firearms.